The invention relates to the field of load-bearing wings, also known by the English term “hydrofoil”, fitted to watercraft. More particularly the invention relates to a retractable load-bearing wing. By “retractable load-bearing wing” is meant any load-bearing wing which can be folded back in such a way that it does not cause any significant increase in the maximum beam of a floating member or hull of a watercraft incorporating such a load-bearing wing.
A load-bearing wing or hydrofoil is a device capable of raising a floating member, also referred to below as a hull, of a watercraft partly or wholly out of the water under one effect of hydrodynamic lift generated on its load-bearing plane by the speed at which the watercraft moves. Because lift is transferred from the hull to the load-bearing plane of the load-bearing wing this device thus makes it possible to reduce drag, that is to say reduce the contact friction between the watercraft and the water, in particular waves. The reduction in drag then makes it possible to reduce the power necessary to achieve a high cruising speed, and therefore to make substantial savings, in particular in terms of fuel consumption.
In the remainder of the description the terms “load-bearing wing” and “hydrofoil” will be used indiscriminately to refer to the same device.
Load-bearing wings are particularly suitable for all watercraft, particularly motorboats of small size, powerboats or even luxury vessels such as, by way of non-limiting examples, yachts. In principle they can be fitted to all kinds of sailing and/or motorboats, single or multihulls or even motor-driven watercraft such as, by way of non-limiting examples, jet skis.
There are different configurations of load-bearing wings. These are classified into two main families: variable surface load-bearing wings which pierce the surface, such as the oblique or “V”-shaped load-bearing wings for example, and load-bearing wings having a constant immersed surface such as upside-down “T”- or “L”-shaped, or even upside-down and “Y”- or “U”-shaped or curved load-bearing wings.
In the case of load-bearing wings which pierce the surface the lift from the wing is proportional to the immersed surface area. Speed compensates for loss of surface area. For a given speed the boat will rise until the lift from the load-bearing plane is equal to the weight applied to said load-bearing plane. Lift is therefore constant, and is said to be self-regulated.
In the case of immersed load-bearing wings the load-bearing surface is wholly immersed at all times. Lift does not vary with the height of rise. Such a configuration is particularly advantageous because of its ability to isolate the boat from the effect of waves. On the other hand this configuration is not naturally stable as regards ride height, pitch and roll. Because of this a load-bearing wing of such type is generally fitted with a stabilizer system. In order to provide stability at any speed the rise height of the load-bearing wing must be capable of being controlled. In order to do this it is suitable to vary the lift coefficient of the load-bearing plane. The stabilizer system thus makes it possible to adjust the angle of incidence, also known as the angle of attack, of the load-bearing plane so as to vary the load-bearing capacity in relation to speed, weight or sea conditions. The stabilizer system may be implemented in different ways, for example by varying the angle of incidence by pivoting the load-bearing plane to incline the leading edge to a greater or lesser extent in relation to the trailing edge, or by using one or more flaps on the trailing edge of the load-bearing plane to make it mobile, or any other similar device for controlling lift.
Load-bearing wings are mounted beneath the hull that they have to support. They nevertheless have a number of disadvantages because of their bulk. Thus a boat fitted with such load-bearing wings is not able to sail at slow speed in shallow water. Mooring alongside a quay or a pontoon is complicated and hazardous, particularly when the load-bearing wing extends beyond the maximum beam of the boat. A boat fitted with load-bearing wings is therefore only able to moor alongside a quay that is intended for it, its vertical wall being inclined so as to be able to allow room for lateral load-bearing wings. In order to prevent them from extending beyond the hull of the boat some load-bearing wings are mounted in a central slot and pass through the hull of the boat vertically, and the height to which they penetrate through the hull varies in relation to the rise height. Such load-bearing wings are for example fitted to the AC72 catamaran designed in 2012 and used in the Americas Cup in 2013. However in the latter case the load-bearing wings generally have a curved profile and the possibilities for constructing profiles of different shape are limited because they are detrimental to the performance and/or cost of the load-bearing wing.
Because the large dimensions of load-bearing wings make mooring in particular very difficult, solutions for retracting them to reduce their dimensions have been envisaged in the past.
Thus document U.S. Pat. No. 7,984,384 describes one solution for retracting a hydrofoil of the immersed type, particularly in the passages in its description on pages 174 and 175 describing FIGS. 398 and 399. The solution described in this document consists of constructing a load-bearing wing which retracts telescopically. In order to do this the support leg of the load-bearing wing slides towards the hull within a sheath, box or slide system referenced 4004a in the document. This sheath system is located within the hull of the boat, which makes it necessary to adjust the boat's hull to a particular configuration of the load-bearing wing. The immersed load-bearing plane comprises a fixed portion located beneath the hull and a retractable portion 4011 which extends beyond the maximum beam of the hull and is capable of sliding within an element 4005 towards the fixed portion 4010 located beneath the hull. Although this system makes it possible to retract a load-bearing wing, it cannot retract it completely so that the boat has the appearance of being without a load-bearing wing. The telescopic retraction system described appears to be complex to construct and requires the hull of the boat to be altered in order to be able to incorporate it. Such a system cannot therefore be easily used on any boat and also cannot be applied to any configuration of load-bearing wing.
Document WO1993/04909 describes a system for damping out the impacts experienced by load-bearing wings, the system applying to both fixed and retractable load-bearing wings. The mechanism for retraction of the load-bearing wing described in this document comprises a motor-driven system rotating an endless screw which engages in a groove provided in the upper surface of the load-bearing wing, while one spherical end of the impact absorption system engages in a groove provided in the opposite surface of the load-bearing wing to cause it to pivot backwards. The angle of retraction is thus controlled by the impact absorption system. The load-bearing wing then pivots and retracts within the hull through a slot made in the hull. This document describes a complex retraction system which again makes it necessary to adapt and modify a boat/s hull and is not able to adapt to all configurations of load-bearing wings. Such a solution is therefore still too complex and costly to be implemented.
Document US 2009/0013917 describes another solution for retracting a load-bearing wing of the immersed type. This solution consists of sliding each support leg supporting a load-bearing plane along a groove formed in the surface of the load-bearing plane on the one hand and along another channel formed in a housing provided beneath the hull of the boat, by means of a piston. The load-bearing plane and the support leg then nest in the housing provided beneath the hull. A vertical guide bar attached beneath the boat's hull acts as a guide when the load-bearing wing is being retracted. This solution also appears to be complex to implement because it requires modification of the boat's hull. It cannot therefore be easily implemented for any type of boat, nor for any configuration of load-bearing wing. Furthermore the presence of the guide bar makes it impossible to reduce the boat's draft.
Other documents such sis documents U.S. Pat. No. 3,241,511, 3,236,202 or 3,044,432 also provide solutions for retracting load-bearing wings that are also based on movements of a telescopic or parallelogram type. Such solutions are complicated and costly to implement, require modifications to boat hulls and cannot always be adapted to all load-bearing wing configurations.
As a consequence the existing solutions are unsatisfactory. In fact although they make it possible to shorten a load-bearing wing, by sliding its constituent elements, which nest and slide within each other, these solutions all require changes in the hull of the watercraft and are not appropriate for all load-bearing wing configurations.